SPEED AND AGILITY

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The life style of the smaller, agile dinosaurs also supports the warm-blooded hypothesis. Whereas modern, cold-blooded reptiles are 'sit and wait' hunters, predatory dinosaurs were active in pursuing and attacking their prey. Such activity requires a high metabolic rate . Some, such as Deinonychus, are believed to have hunted at night - highly unlikely for a cold-blooded creature.
All theropods and many other dinosaur types were bipedal , an obligation which requires more metabolic energy than a sprawling, four-legged posture. Some commentators go so far as to say that bipedalism cannot be attained without some form of endothermy.
Dinosaurs also put a lot of evolutionary energy into sexual display and territorial intimidatory display (head butting, ornamental head crests, 'sails' on backs etc) which is far more characteristic of warm-blooded animals than cold.
The average walking speed of today's mammals is much higher than that of cold-blooded animals. Their speeds can actually be measured, and can also be calculated from their footprints. Using the footprint calculations on prehistoric mammals we get speeds the same as present day mammals, whereas the cold-blooded reptiles and amphibians of the Coal Age are much slower (1 -2 mph/3 - 6 kph). Dinosaurs and thecodonts , on the other hand, appear to have been just as fast as mammals, a conclusion supported by their fossil skeletons. Their limbs were built for speed and prolonged exercise.
The ability to be fast and agile for an extended period requires a high metabolic rate and thus a large heart and efficient lungs. Such organs do not, of course, fossilize, but most dinosaur skeletons have a much wider body space in the chest region when compared with cold-blooded reptiles and could easily have accomodated large hearts and lungs. The hadrosaurs and horned dinosaurs do not show such enlargement, but neither do some birds - they compensate by having a series of air sacs throughout the vertebrae and in body spaces that are connected to the lungs. Air flows continually in one direction instead of breathing in and out, and the blood flows in the opposite direction at gas exchange areas, leading to an extremely efficient system for providing oxygen and removing waste gases. Most dinosaurs also show such air sacs in the backbone, and may well have had body sacs also.
It has been suggested (as argued above), that sustained activity and obligatory bipedalism , as exhibited by dinosaurs and birds, requires an endothermic metabolism. Similarly, some writers refer to the wide range of relative brain size of dinosaurs. At the top end of their range they approach birds and mammals, and in theory this requires an abundant oxygen supply to the brain, in turn implying a high respiratory rate and high metabolic rate.
Some authorities suggest that for animals of the size and apparent vigorous life-style of dinosaurs, sufficient heat will be generated by the maintainence of hich activity levels to make the animals effective endotherms, regardless of the presence or absence of any specific mechanisms.

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